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    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav>  <ul class="sidebar-links"><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>MySQL笔记</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/noteslibrary/pages/32e9fd/" class="sidebar-link">写在前面</a></li><li><a href="/noteslibrary/pages/cfda94/" class="sidebar-link">数据库概述</a></li><li><a href="/noteslibrary/pages/497bcb/" class="sidebar-link">MySQL环境搭建</a></li><li><a href="/noteslibrary/pages/9c9f3a/" class="sidebar-link">基本的SELECT语句</a></li><li><a href="/noteslibrary/pages/b59830/" class="sidebar-link">运算符</a></li><li><a href="/noteslibrary/pages/6fef5b/" class="sidebar-link">排序与分页</a></li><li><a href="/noteslibrary/pages/3a50a8/" class="sidebar-link">多表查询</a></li><li><a href="/noteslibrary/pages/8de5b4/" aria-current="page" class="active sidebar-link">单行函数</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_1-函数的理解" class="sidebar-link">1. 函数的理解</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_1-1-什么是函数" class="sidebar-link">1.1 什么是函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_1-2-不同dbms函数的差异" class="sidebar-link">1.2 不同DBMS函数的差异</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_1-3-mysql的内置函数及分类" class="sidebar-link">1.3 MySQL的内置函数及分类</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_2-数值函数" class="sidebar-link">2. 数值函数</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_2-1-基本函数" class="sidebar-link">2.1 基本函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_2-2-角度与弧度互换函数" class="sidebar-link">2.2 角度与弧度互换函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_2-3-三角函数" class="sidebar-link">2.3 三角函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_2-4-指数与对数" class="sidebar-link">2.4 指数与对数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_2-5-进制间的转换" class="sidebar-link">2.5 进制间的转换</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_3-字符串函数" class="sidebar-link">3. 字符串函数</a></li><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_4-日期和时间函数" class="sidebar-link">4. 日期和时间函数</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_4-1-获取日期、时间" class="sidebar-link">4.1 获取日期、时间</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_4-2-日期与时间戳的转换" class="sidebar-link">4.2 日期与时间戳的转换</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_4-3-获取月份、星期、星期数、天数等函数" class="sidebar-link">4.3 获取月份、星期、星期数、天数等函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_4-4-日期的操作函数" class="sidebar-link">4.4 日期的操作函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_4-5-时间和秒钟转换的函数" class="sidebar-link">4.5 时间和秒钟转换的函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_4-6-计算日期和时间的函数" class="sidebar-link">4.6 计算日期和时间的函数</a></li><li class="sidebar-sub-header level3"><a href="/noteslibrary/pages/8de5b4/#_4-7-日期的格式化与解析" class="sidebar-link">4.7 日期的格式化与解析</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_5-流程控制函数" class="sidebar-link">5. 流程控制函数</a></li><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_6-加密与解密函数" class="sidebar-link">6. 加密与解密函数</a></li><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_7-mysql信息函数" class="sidebar-link">7. MySQL信息函数</a></li><li class="sidebar-sub-header level2"><a href="/noteslibrary/pages/8de5b4/#_8-其他函数" class="sidebar-link">8. 其他函数</a></li></ul></li><li><a href="/noteslibrary/pages/2dfe6d/" class="sidebar-link">聚合函数</a></li><li><a href="/noteslibrary/pages/3ea5ac/" class="sidebar-link">子查询</a></li><li><a href="/noteslibrary/pages/70a90b/" class="sidebar-link">创建和管理表</a></li><li><a href="/noteslibrary/pages/a20c5b/" class="sidebar-link">数据处理之增删改</a></li><li><a href="/noteslibrary/pages/9515c0/" class="sidebar-link">MySQL数据类型精讲</a></li><li><a href="/noteslibrary/pages/98e681/" class="sidebar-link">约束</a></li><li><a href="/noteslibrary/pages/4535e0/" class="sidebar-link">视图</a></li><li><a href="/noteslibrary/pages/e5e604/" class="sidebar-link">存储过程与函数</a></li><li><a href="/noteslibrary/pages/f68b46/" class="sidebar-link">变量与流程控制与游标</a></li><li><a href="/noteslibrary/pages/fe941e/" class="sidebar-link">触发器</a></li><li><a href="/noteslibrary/pages/efad7b/" class="sidebar-link">MySQL8其它新特性</a></li></ul></section></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/noteslibrary/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><a href="/noteslibrary/database/#数据库" data-v-06225672>数据库</a></li><li data-v-06225672><a href="/noteslibrary/database/#MySQL笔记" data-v-06225672>MySQL笔记</a></li></ul> <div class="info" data-v-06225672><!----> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-04-05</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">单行函数<!----></h1> <!----> <div class="theme-vdoing-content content__default"><h1 id="单行函数"><a href="#单行函数" class="header-anchor">#</a> 单行函数</h1> <h2 id="_1-函数的理解"><a href="#_1-函数的理解" class="header-anchor">#</a> 1. 函数的理解</h2> <h3 id="_1-1-什么是函数"><a href="#_1-1-什么是函数" class="header-anchor">#</a> 1.1 什么是函数</h3> <p>函数在计算机语言的使用中贯穿始终，函数的作用是什么呢？它可以把我们经常使用的代码封装起来，需要的时候直接调用即可。这样既 <code>提高了代码效率</code> ，又 <code>提高了可维护性</code> 。在 SQL 中我们也可以使用函数对检索出来的数据进行函数操作。使用这些函数，可以极大地 <code>提高用户对数据库的管理效率</code> 。</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840190.png" alt="image-20220214175041724"> <p>从函数定义的角度出发，我们可以将函数分成 <code>内置函数</code> 和 <code>自定义函数</code> 。在 SQL 语言中，同样也包括了内置函数和自定义函数。内置函数是系统内置的通用函数，而自定义函数是我们根据自己的需要编写的，本章及下一章讲解的是 SQL 的内置函数。</p> <h3 id="_1-2-不同dbms函数的差异"><a href="#_1-2-不同dbms函数的差异" class="header-anchor">#</a> 1.2 不同DBMS函数的差异</h3> <p>我们在使用 SQL 语言的时候，不是直接和这门语言打交道，而是通过它使用不同的数据库软件，即DBMS。<strong>DBMS 之间的差异性很大，远大于同一个语言不同版本之间的差异</strong>。实际上，只有很少的函数是被 DBMS 同时支持的。比如，大多数 DBMS 使用（||）或者（+）来做拼接符，而在 MySQL 中的字符串拼接函数为concat()。大部分 DBMS 会有自己特定的函数，这就意味着<strong>采用 SQL 函数的代码可移植性是很差的</strong>，因此在使用函数的时候需要特别注意。</p> <h3 id="_1-3-mysql的内置函数及分类"><a href="#_1-3-mysql的内置函数及分类" class="header-anchor">#</a> 1.3 MySQL的内置函数及分类</h3> <p>MySQL提供了丰富的内置函数，这些函数使得数据的维护与管理更加方便，能够更好地提供数据的分析与统计功能，在一定程度上提高了开发人员进行数据分析与统计的效率。
MySQL提供的内置函数从 <code>实现的功能角度</code> 可以分为<code>数值函数、字符串函数、日期和时间函数、流程控制函数、加密与解密函数、获取MySQL信息函数、聚合函数</code>等。这里，我将这些丰富的内置函数再分为两类： <strong>单行函数 、 聚合函数（或分组函数）</strong> 。</p> <p><strong>两种SQL函数</strong></p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840191.png" alt="image-20220214183812003"> <p><strong>单行函数</strong></p> <ul><li>操作数据对象</li> <li>接受参数返回一个结果</li> <li><strong>只对一行进行变换</strong></li> <li><strong>每行返回一个结果</strong></li> <li>可以嵌套</li> <li>参数可以是一列或一个值</li></ul> <h2 id="_2-数值函数"><a href="#_2-数值函数" class="header-anchor">#</a> 2. 数值函数</h2> <h3 id="_2-1-基本函数"><a href="#_2-1-基本函数" class="header-anchor">#</a> 2.1 基本函数</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840192.png" alt="image-20220214183942846"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840193.png" alt="image-20220214184100243"> <h3 id="_2-2-角度与弧度互换函数"><a href="#_2-2-角度与弧度互换函数" class="header-anchor">#</a> 2.2 角度与弧度互换函数</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840194.png" alt="image-20220214184132244"> <h3 id="_2-3-三角函数"><a href="#_2-3-三角函数" class="header-anchor">#</a> 2.3 三角函数</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840195.png" alt="image-20220214184159555"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840196.png" alt="image-20220214184226615"> <h3 id="_2-4-指数与对数"><a href="#_2-4-指数与对数" class="header-anchor">#</a> 2.4 指数与对数</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840197.png" alt="image-20220214184259763"> <h3 id="_2-5-进制间的转换"><a href="#_2-5-进制间的转换" class="header-anchor">#</a> 2.5 进制间的转换</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840198.png" alt="image-20220214184325914" style="zoom:100%;"> <h2 id="_3-字符串函数"><a href="#_3-字符串函数" class="header-anchor">#</a> 3. 字符串函数</h2> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840199.png" alt="image-20220214204500316" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840200.png" alt="image-20220214204534164" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840201.png" alt="image-20220214204559552" style="zoom:100%;"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840202.png" alt="image-20220214201810952" style="zoom:100%;"> <h2 id="_4-日期和时间函数"><a href="#_4-日期和时间函数" class="header-anchor">#</a> 4. 日期和时间函数</h2> <h3 id="_4-1-获取日期、时间"><a href="#_4-1-获取日期、时间" class="header-anchor">#</a> 4.1 获取日期、时间</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840203.png" alt="image-20220214201856422" style="zoom:100%;"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840204.png" alt="image-20220214201926330" style="zoom:100%;"> <h3 id="_4-2-日期与时间戳的转换"><a href="#_4-2-日期与时间戳的转换" class="header-anchor">#</a> 4.2 日期与时间戳的转换</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840205.png" alt="image-20220214202009211" style="zoom:100%;"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840206.png" alt="image-20220214202108165" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840207.png" alt="image-20220214202135761" style="zoom:100%;"> <h3 id="_4-3-获取月份、星期、星期数、天数等函数"><a href="#_4-3-获取月份、星期、星期数、天数等函数" class="header-anchor">#</a> 4.3 获取月份、星期、星期数、天数等函数</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840208.png" alt="image-20220214202215153" style="zoom:100%;"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840209.png" alt="image-20220214202312453" style="zoom:100%;"> <h3 id="_4-4-日期的操作函数"><a href="#_4-4-日期的操作函数" class="header-anchor">#</a> 4.4 日期的操作函数</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840210.png" alt="image-20220214202411541" style="zoom:100%;"> <h3 id="_4-5-时间和秒钟转换的函数"><a href="#_4-5-时间和秒钟转换的函数" class="header-anchor">#</a> 4.5 时间和秒钟转换的函数</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840211.png" alt="image-20220214202436251" style="zoom:100%;"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840212.png" alt="image-20220214202512153" style="zoom:100%;"> <h3 id="_4-6-计算日期和时间的函数"><a href="#_4-6-计算日期和时间的函数" class="header-anchor">#</a> 4.6 计算日期和时间的函数</h3> <p><strong>第1组：</strong></p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840213.png" alt="image-20220214202616614" style="zoom:100%;"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840214.png" alt="image-20220214202708471" style="zoom:100%;"> <p><strong>第2组：</strong></p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840215.png" alt="image-20220214202742204" style="zoom:100%;"> <p>举例：</p> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840216.png" alt="image-20220214202818704" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840218.png" alt="image-20220214203002927" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840219.png" alt="image-20220214203051043" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840220.png" alt="image-20220214203124004" style="zoom:100%;"> <h3 id="_4-7-日期的格式化与解析"><a href="#_4-7-日期的格式化与解析" class="header-anchor">#</a> 4.7 日期的格式化与解析</h3> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840221.png" alt="image-20220214203156765" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840222.png" alt="image-20220214203257844" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840223.png" alt="image-20220214203433454" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840224.png" alt="image-20220214203537453" style="zoom:100%;"> <h2 id="_5-流程控制函数"><a href="#_5-流程控制函数" class="header-anchor">#</a> 5. 流程控制函数</h2> <blockquote><p>流程处理函数可以根据不同的条件，执行不同的处理流程，可以在SQL语句中实现不同的条件选择。MySQL中的流程处理函数主要包括IF()、IFNULL()和CASE()函数。</p></blockquote> <h2 id="_6-加密与解密函数"><a href="#_6-加密与解密函数" class="header-anchor">#</a> 6. 加密与解密函数</h2> <blockquote><p>加密与解密函数主要用于对数据库中的数据进行加密和解密处理，以防止数据被他人窃取。这些函数在保证数据库安全时非常有用。</p></blockquote> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840225.png" alt="image-20220214203935424" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840226.png" alt="image-20220214203958383" style="zoom:100%;"> <h2 id="_7-mysql信息函数"><a href="#_7-mysql信息函数" class="header-anchor">#</a> 7. MySQL信息函数</h2> <blockquote><p>MySQL中内置了一些可以查询MySQL信息的函数，这些函数主要用于帮助数据库开发或运维人员更好地对数据库进行维护工作。</p></blockquote> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840227.png" alt="image-20220214204026325" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840228.png" alt="image-20220214204108375" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840229.png" alt="image-20220214204138395" style="zoom:100%;"> <h2 id="_8-其他函数"><a href="#_8-其他函数" class="header-anchor">#</a> 8. 其他函数</h2> <blockquote><p>MySQL中有些函数无法对其进行具体的分类，但是这些函数在MySQL的开发和运维过程中也是不容忽视的。</p></blockquote> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840230.png" alt="image-20220214204214637" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840231.png" alt="image-20220214204258804" style="zoom:100%;"> <img src="https://lcfimgsbed.oss-cn-chengdu.aliyuncs.com/img/202207250840232.png" alt="image-20220214204336374" style="zoom:100%;"></div></div> <!----> <div class="page-edit"><div class="edit-link"><a href="https://github.com/lcfqzd/vuepress-theme-vdoing/edit/master/docs/04.数据库/01.MySQL笔记/07.单行函数.md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <div class="tags"><a href="/noteslibrary/tags/?tag=MySQL" title="标签">#MySQL</a></div> <!----></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/noteslibrary/pages/3a50a8/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">多表查询</div></a> <a href="/noteslibrary/pages/2dfe6d/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">聚合函数</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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